Field of the Invention
The present invention relates to gate drivers.
Description of the Related Art
As a power device that is a semiconductor device used in a power converter such as a converter or an inverter, an SiC (silicon carbide) power device is currently being developed. The SiC power device is considered to be a key device in the next generation power electronics due to its physical superiority, and is being put into commercial use.
As compared with a Si power device, the SiC power device has superior physical properties such as a high breakdown voltage, a low on-resistance, a high-speed switching characteristic and a high-temperature resistance characteristic. In particular, it is very important for reducing the size of a power converter itself to realize high-speed switching because this leads to the miniaturization of constituent components such as a capacitor, an inductor and a transformer which occupy a large volume of the power converter.
However, at present, the development of a gate driver (gate drive circuit) that performs high-speed switching drive on the SiC power device is not realized (examples of a conventional technology related to the gate driver include patent documents 1 to 5 below). Although a conventional Si (silicon) power device mainly deals with frequencies of up to about a few hundred kHz, and there are gate drivers suitable for driving Si power devices of up to such frequencies, a gate driver suitable for the SiC power device is not developed.
<Patent document 1> Japanese Unexamined Patent Application Publication No. 2014-147237
<Patent document 2> Japanese Unexamined Patent Application Publication No. 2013-243877
<Patent document 3> Japanese Unexamined Patent Application Publication No. 2014-57491
<Patent document 4> Japanese Patent No. 5400968
<Patent document 5> Japanese Patent No. 2886495
A Si-based CMOS circuit for driving an FET (field-effect transistor) at high frequencies is well known. However, in the CMOS circuit, the signal application is limited, and in order to drive, at a high speed, the SiC power device provided in the power converter, large charge transfer for a large input capacity is instantaneously needed, with the result that it is impossible to achieve driving with the CMOS circuit without being processed. Driving with the CMOS circuit causes a greater loss, and thus it is impossible to take advantage of the superiority of the SiC power device.
In order to take advantage of the physical properties of a wideband gap semiconductor such as the SiC power device, in the driving thereof, it is necessary to use an element having such a property as to take advantage of the properties, and thus it can be considered that an element formed of GaN (gallium nitride) or SiC is used to realize the CMOS circuit. However, both in GaN and SiC, only an n-type MOSFET is currently being developed, and consideration is not given to the CMOS circuit of a bridge structure that cannot be achieved without realizing a p-type MOSFET. Even when a p-type MOSFET is realized, since the mobility of holes of SiC or GaN is significantly lower than that of electrons, it is unlikely that it is possible to realize a CMOS circuit which can be driven at a high speed.
Although a circuit mounting technology for reducing noises caused by driving at frequencies of up to a few hundred kHz used often in power electronics or at frequencies of a GHz band used in high-speed communication is currently developed, a circuit technology for driving in a few to a few hundred MHz band which can be used in power electronics is not developed except a circuit for dealing with extremely low power of about a few watts or the technological level thereof is significantly immature. Hence, in reality, it is common to avoid such high-frequency driving. However, if a drive circuit for driving in a few to a few hundred MHz band is developed, it is expected that the development of technology for reducing noises will progress.
As described above, the inventors of the present application uniquely focus attention on the conditions in which at present, the driving of a power device at frequencies of a few to a few hundred MHz is not realized.